Al-casting alloy

ABSTRACT

The invention relates to an Al casting alloy.

The invention relates to an aluminum casting alloy.

DE 10 2008 055 928 A1, DE 10 2012 108 590 A, DE 10 2013 108 127 A1 andDE 10 2014 101 317 A1 disclose various low-Si Al casting alloys.

Proceeding from this prior art, it is an object of the present inventionto provide an improved low-Si Al casting alloy which has especially beenfurther developed with regard to its mechanical properties.

This is achieved in accordance with the invention by an Al casting alloycontaining at least five of the following alloy constituents:

Si: 3.0% to 3.8% by weightMg: 0.3% to 0.8% by weightCr: 0.05% to 0.35% by weightFe: <0.18% by weightMn: <0.06% by weightTi: <0.16% by weightCu: 0.006-0.015% by weightSr: 0.010 to 0.030% by weightZr<0.006% by weightZn<0.006% by weightImpurities: <0.1% by weightand is supplemented by Al to an extent of 100% by weight in each case.

Such an Al casting alloy is stronger, tougher and more ductile comparedto the prior art.

The inventive selection of alloy constituents in the order of magnitudespecified leads to a further significant improvement in the mechanicalproperties which is already apparent in the cast state, but especiallyin a cast component after a 2-stage heat treatment, namely a solutionannealing operation and a subsequent age hardening operation, withpreferable provision of quenching of the cast component in water betweenthese two heat treatment steps. For chassis applications, preferably forwheel-bearing components, very preferably for damper stilts, wheelbearings and especially swivel bearings, but also for control arms, theresult is an overall increase in mechanical indices.

Entirely unexpectedly, especially in relation to the mechanical index ofelongation at break A5, it has been found that the upper limit specifiedas critical for copper in DE 10 2013 108 127 A1 of 0.006% by weight isexceeded in a manner essential to the invention.

For optimization of the mechanical indices, it may be advantageous whenCu is present with a content of more than 0.006% by weight, preferablyof more than 0.007% by weight, more preferably of more than 0.008% byweight, most preferably at least 0.009% by weight. For optimization ofthe mechanical indices, it may be advantageous when Cu is present with acontent of less than 0.015% by weight, preferably of less than 0.013% byweight, more preferably of less than 0.012% by weight, most preferablyof less than 0.011% by weight.

The alloys of the invention may contain impurities resulting from thepreparation, for example Pb, Ni, etc., as is common knowledge to theperson skilled in the art.

For optimization of the mechanical indices, it may be advantageous whenSi is present with a content of more than 3.1% by weight, preferably ofmore than 3.3% by weight, more preferably of more than 3.4% by weight.For optimization of the mechanical indices, it may be advantageous whenSi is present with a content of less than 3.7% by weight, preferably ofless than 3.5% by weight.

It may be advantageous for particular applications when Si is presentwith a content of more than 3.3% to less than 3.7% by weight. For someother applications, it may be advantageous when Si is present with acontent of more than 3.0% to less than 3.3% by weight.

For optimization of the mechanical indices, it may be advantageous whenMg is present with a content of more than 0.40% by weight, preferably ofmore than 0.50% by weight, more preferably of more than 0.55% by weight.For optimization of the mechanical indices, it may be advantageous whenMg is present with a content of less than 0.70% by weight, preferably ofless 0.60% by weight.

For optimization of the mechanical indices, it may be advantageous whenCr is present with a content of more than 0.10% by weight, preferably ofmore than 0.15% by weight, more preferably of more than 0.20% by weight,most preferably of more than 0.25% by weight. For optimization of themechanical indices, it may be advantageous when Cr is present with acontent of at most 0.30% by weight, preferably of less than 0.30% byweight.

For optimization of the mechanical indices, it may be advantageous whenFe is present with a content of more than 0.01% by weight, preferably ofmore than 0.05% by weight, more preferably of more than 0.07% by weight.For optimization of the mechanical indices, it may be advantageous whenFe is present with a content of less than 0.15% by weight, preferably ofless than 0.12% by weight.

For optimization of the mechanical indices, it may be advantageous whenMn is present with a content of more than 0.01% by weight, preferably ofmore than 0.02% by weight. For optimization of the mechanical indices,it may be advantageous when Mn is present with a content less than 0.15%by weight, preferably of less than 0.12% by weight, more preferably ofless than 0.10% by weight.

For optimization of the mechanical indices, it may be advantageous whenTi is present with a content of more than 0.01% by weight, preferably ofmore than 0.03% by weight, more preferably of more than 0.04% by weight.For optimization of the mechanical indices, it may be advantageous whenTi is present with a content of less than 0.10% by weight, preferably ofless than 0.08% by weight, more preferably of less than 0.065% byweight, most preferably of less than 0.055% by weight.

For optimization of the mechanical indices, it may be advantageous whenSr is present with a content of more than 0.015% by weight, preferablyof more than 0.020% by weight. For optimization of the mechanicalindices, it may be advantageous when Sr is present with a content ofless than 0.030% by weight, preferably of less than 0.025% by weight.

For optimization of the mechanical indices, it may be advantageous whenZr is present with a content of more than 0.001% by weight. Foroptimization of the mechanical indices, it may be advantageous when Zris present with a content of less than 0.005% by weight, preferably ofless than 0.004% by weight, more preferably of less than 0.003% byweight.

For optimization of the mechanical indices, it may be advantageous whenZn is present with a content of more than 0.001% by weight, preferablyof more than 0.002% by weight. For optimization of the mechanicalindices, it may be advantageous when Zn is present with a content ofless than 0.005% by weight, preferably of less than 0.004% by weight.

For numerous applications, it may be advantageous when impurities arepresent with a content of less than 0.05% by weight, preferably lessthan 0.035% by weight.

For certain cast components, it has been found to be advantageous whenthe Al casting alloy of the invention is a low-pressure casting Alalloy.

Accordingly, the invention also relates to a method of producing a castcomponent from an Al casting alloy as claimed in any of claims 1 to 22,in which the low-pressure casting method is employed.

For particular cast components, it has been found to be advantageouswhen the Al casting alloy is a counterpressure casting (CPC) Al alloy.

Accordingly, the invention also relates to a method of producing a castcomponent from an Al casting alloy as claimed in any of claims 1 to 22,in which the low-pressure counterpressure casting method is employed.

Various permanent mold casting methods are suitable in principle asmanufacturing methods for cast components, especially as chassis parts,preferably as wheel-bearing components, very preferably as damperstilts, wheel bearings or swivel bearings, of motor vehicles made fromthe cast alloy of the invention. Owing to the very good mechanicalproperties in the case of highly stressed wheel-bearing parts of motorvehicles, however, particularly low-pressure diecasting and thecounterpressure casting (CPC) method, which is also referred to as thecounterpressure diecasting method, are suitable as manufacturingmethods.

Manufacturing methods employed for cast components, especially aschassis parts, preferably as wheel-bearing components, very preferablyas damper stilts, wheel bearings or swivel bearings, of motor vehiclesmade from the cast alloy of the invention may advantageously besqueeze-casting, gravity diecasting or pressure diecasting, especiallythixocasting, rheocasting or low-pressure sand casting.

In order to achieve or even further develop the abovementionedadvantages, it is advantageous when the cast components are subjected toa two-stage heat treatment, namely a solution annealing operation and asubsequent age hardening operation. It may be advantageous when the castcomponent is quenched in water between the two heat treatment stages.

It may be appropriate when the cast component after the castingoperation is solution-annealed between 530° C. and 550° C. for 6 to 10h, preferably between 540° C. and 550° C. for 7 to 9 h, especially for 8to 9 h, most preferably between more than 540° C. and 550° C. for 7 to 9h, especially for 8 to 9 h.

It may be appropriate when the cast component after the castingoperation is tempered between 180° C. and 210° C. for 1 to 8 h,especially for 1 to 6.5 h, preferably between 180° C. and 190° C. for 1to 6.5 h, especially for 4 to 6.5 h, more preferably between 180° C. andless than 190° C. for 4 to 6.5 h, especially for 5 to 6.5 h.

The invention further provides for the use of an Al casting alloy asclaimed in any of the claims or of a cast component, especially one thathas been heat-treated, as claimed in any of the claims for chassis partsof motor vehicles, preferably for wheel-bearing components of motorvehicles, most preferably for damper stilts, wheel bearings or swivelbearings of motor vehicles.

According to the invention, the cast components have an improvedstrength/strain ratio coupled with improved microstructure properties.The casting method firstly enables a casting free of larger defects,known as craters; secondly, the microstructure is positively affected insuch a way that the number of inner indentations that reduce elongationat break is kept to a minimum.

As already mentioned, the Al casting alloy of the invention has beenfound to be especially suitable particularly for components underrelatively high stress, such as damper stilts, wheel bearings or swivelbearings. A very preferred process for production of such relativelyhighly stressed components is the counterpressure diecasting (CPC)method.

Cast components of the invention that have been produced from an Alcasting alloy as claimed in any of the claims and/or by a method asclaimed in any of the claims feature, after a heat treatment, a yieldpoint R_(P)0.2 of 300 to 330 MPa, preferably of >320 to 330 MPa, and/oran elongation at break A5 of 7% to 11%, preferably of 8.5% to 10%, morepreferably of 9% to 9.5%, and/or a tensile strength R_(m) of 350-375MPa, preferably of >360-375 MPa.

EXAMPLE

To ascertain the mechanical properties of an alloy of the inventioncontaining 3.4% by weight of Si, 0.6% by weight of Mg, 0.27% by weightof Cr, 0.09% by weight of Fe, 0.03% by weight of Mn, 0.05% by weight ofTi, 0.009% by weight of Cu, 0.022% by weight of Sr, 0.002% by weight ofZr, 0.003% by weight of Zn and impurities of less than 0.1% by weight,in each case supplemented to 100% by weight with Al, what is called a“French tensile specimen” according to DIN 50125 is cut out of a swivelbearing produced by means of a counterpressure diecasting (CPC) method,the swivel bearing having received a heat treatment (solution annealingat 540° C. for 8 h, quenching in water, age hardening at 180° C. for 6.5h) beforehand. The casting of comparative examples (AlSi3Mg0.5 andAlSi3Mg0.5Cr0.3) and subsequent heat treatment are effected under thesame conditions. The alloys to be compared differ solely in the chromiumcontent. The specimen is taken at the same position in the swivelbearing. The mechanical properties of tensile strength R_(m), yieldpoint R_(p)0.2 and elongation at break A5 according to DIN10002 areascertained.

R_(m) [MPa] R_(p)0.2 [MPa] A5 [%] AlSi3Mg0.5 327 263 9.3 Alloy of theinvention 369 322 9.12 AlSi3Mg0.5Cr0.3 358 308 6.9

Against the background of DE 10 2013 108 127 A1 and the upper limit forcopper of 0.006% by weight which is specified as critical for themechanical indices, the achievement of the abovementioned mechanicalindices for the alloy of the invention was not to be expected.

1. An Al casting alloy containing at least five of the following alloyconstituents: Si: 3.0% to 3.8% by weight Mg: 0.3% to 0.8% by weight Cr:0.05% to 0.35% by weight Fe: <0.18% by weight Mn: <0.06% by weight Ti:<0.16% by weight Cu: 0.006-0.015% by weight Sr: 0.010% to 0.030% byweight Zr<0.006% by weight Zn<0.006% by weight Impurities: <0.1% byweight and is supplemented by Al to an extent of 100% by weight in eachcase.
 2. The Al casting alloy as claimed in claim 1, wherein Si ispresent with a content of more than 3.1% by weight, preferably of morethan 3.3% by weight, more preferably of more than 3.4% by weight.
 3. TheAl casting alloy as claimed in claim 1, wherein Si is present with acontent of less than 3.7% by weight, preferably of less than 3.5% byweight.
 4. The Al casting alloy as claimed in claim 1, wherein Mg ispresent with a content of more than 0.40% by weight, preferably of morethan 0.50% by weight, more preferably of more than 0.55% by weight. 5.The Al casting alloy as claimed in claim 1, wherein Mg is present with acontent of less than 0.70% by weight, preferably of less 0.60% byweight.
 6. The Al casting alloy as claimed in claim 1, wherein Cr ispresent with a content of more than 0.10% by weight, preferably of morethan 0.15% by weight, more preferably of more than 0.20% by weight, mostpreferably of more than 0.25% by weight.
 7. The Al casting alloy asclaimed in claim 1, wherein Cr is present with a content of at most0.30% by weight, preferably of less than 0.30% by weight.
 8. The Alcasting alloy as claimed in claim 1, wherein Fe is present with acontent of more than 0.01% by weight, preferably of more than 0.05% byweight, more preferably of more than 0.07% by weight.
 9. The Al castingalloy as claimed claim 1, wherein Fe is present with a content of lessthan 0.15% by weight, preferably of less than 0.12% by weight.
 10. TheAl casting alloy as claimed in claim 1, wherein Mn is present with acontent of more than 0.01% by weight, preferably of more than 0.02% byweight.
 11. The Al casting alloy as claimed in claim 1, wherein Mn ispresent with a content less than 0.15% by weight, preferably of lessthan 0.12% by weight, more preferably of less than 0.10% by weight. 12.The Al casting alloy as claimed in claim 1, wherein Ti is present with acontent of more than 0.01% by weight, preferably of more than 0.03% byweight, more preferably of more than 0.04% by weight.
 13. The Al castingalloy as claimed in claim 1, wherein Ti is present with a content ofless than 0.10% by weight, preferably of less than 0.08% by weight, morepreferably of less than 0.065% by weight, most preferably of less than0.055% by weight.
 14. The Al casting alloy as claimed in claim 1,wherein Cu is present with a content of more than 0.006% by weight,preferably of more than 0.007% by weight, more preferably of more than0.008% by weight, most preferably at least 0.009% by weight.
 15. The Alcasting alloy as claimed in claim 1, wherein Cu is present with acontent of less than 0.015% by weight, preferably of less than 0.013% byweight, more preferably of less than 0.012% by weight, most preferablyof less than 0.011% by weight.
 16. The Al casting alloy as claimed inclaim 1, wherein Sr is present with a content of more than 0.015% byweight, preferably of more than 0.020% by weight.
 17. The Al castingalloy as claimed in claim 1, wherein Sr is present with a content ofless than 0.030% by weight, preferably of less than 0.025% by weight.18. The Al casting alloy as claimed in claim 1, wherein Zr is presentwith a content of more than 0.001% by weight.
 19. The Al casting alloyas claimed in claim 1, wherein Zr is present with a content of less than0.005% by weight, preferably of less than 0.004% by weight, morepreferably of less than 0.003% by weight.
 20. The Al casting alloy asclaimed in claim 1, wherein Zn is present with a content of more than0.001% by weight, preferably of more than 0.002% by weight.
 21. The Alcasting alloy as claimed in claim 1, wherein Zn is present with acontent of less than 0.005% by weight, preferably of less than 0.004% byweight.
 22. The Al casting alloy as claimed in claim 1, whereinimpurities are present with a content of less than 0.05% by weight,preferably less than 0.035% by weight. 23-32. (canceled)
 33. A castcomponent produced from an Al casting alloy as claimed in claim 1,wherein the cast component after a heat treatment has a yield pointR_(P)0.2 of 300 to 330 MPa, preferably of >320 to 330 MPa, and/or anelongation at break A5 of 7% to 11%, preferably of 8.5% to 10%, morepreferably of 9% to 9.5%, and/or a tensile strength R_(m) of 350-375MPa, preferably of >360-375 MPa.